1. Field of the Invention
The present invention relates, in general, to a method of manufacturing a printed circuit board (PCB). More particularly, the present invention relates to a method of manufacturing a PCB, in which a dummy metal frame enclosing the outer periphery of a product part is left in place until the completion of a product, so that, during the formation of circuits, the rigidity of the PCB is assured and the generation of defects due to warping is minimized.
2. Description of the Related Art
In order for technology to keep up with the trend of increasing the signal transmission speed and the density of semiconductor chips, the demand for flip chip mounting, by which a semiconductor is directly mounted on a substrate, is increasing, replacing conventional CSP mounting and wire bonding mounting. Although flip chip mounting requires a highly reliable substrate having high density, an increase in the specification of the substrate in proportion to the increase in the density of the semiconductor is almost impossible to achieve in practice. Thus, there is an urgent need for the development of next-generation techniques for promoting flip chip mounting in the future.
The specification required for a flip chip mounting substrate is closely related to the specification of a semiconductor and requirements of high speed and high degree in electronic markets, and there are many goals to be realized, including circuit fineness, good electrical properties, high reliability, fast signal transmission, and high functionality. However, high performance of semiconductors results in heat generation, which is regarded as a big mechanical problem. To solve this, attempts to improve performance using multi-core architecture have been made, in place of a conventional approach of increasing the clock speed. As the results thereof, signal I/O is greatly increased, and hence, there is a need to remarkably increase the circuit density of a substrate for mounting a semiconductor. Further, with the aim of mitigating the heat generation, there is an increasing need to limit impedance in a substrate on which a semiconductor is mounted in order to minimize power loss. Accordingly, for the specification required for the substrate described above, the development of elementary techniques for realizing fine circuits, fine pitch bumps, fine pitch stacked vias, and low impedance, and the development of novel processes and novel material for inexpensive fabrication are required.
In this regard, the process of manufacturing a PCB according to a conventional technique is sequentially illustrated in FIGS. 3A to 3L, and is described below.
A resin substrate 301 having copper foil layers 302 formed on both surfaces thereof is subjected to half-etching, thus decreasing the thickness of the copper foil layers 302, after which through holes 303 are formed therein by means of typical etching and drilling (FIGS. 3A to 3C). Subsequently, an electroless copper plating layer 304 and a copper electroplating layer 305 are formed on the substrate having the through holes 303 (FIGS. 3D and 3E). The through holes 303 are filled with a conductive paste 306 (FIG. 3F), and then an inner circuit pattern is formed using patterning (FIG. 3G). Next, insulating layers 307 and via holes 308 are sequentially formed (FIGS. 3H and 3I), and then an outer circuit pattern is formed (FIG. 3J). Subsequently, solder resist layers 310 are formed, and then openings are formed in the solder resist layers 310 through a solder opening process, thus allowing soldering pads 309 to be exposed. Then, solder balls 311 are mounted on the exposed soldering pads 309, after which contour routing is conducted, thereby forming unit PCBs (FIGS. 3K and 3L).
According to the conventional method of manufacturing the flip chip mounting substrate, the core material having a thickness of from 0.4 mm to 0.8 mm is processed to form through holes and circuits, after which, on both sides of the core thus processed, acting as a base plate, formation of insulating layers, via processing, copper plating, and circuit formation are repeatedly conducted, thus building up the layers, thereby manufacturing a substrate having a high density structure. However, in the case where a coreless substrate, such as an ultra-thin substrate, is manufactured using the conventional method, the following two problems are incurred.
First, when a substrate having low rigidity without a base plate is formed into a built-up structure by repeating the formation of insulating layers, interlayer connection processing, and the formation of circuits using conventional equipment, many process defects, including the dropping of the substrate from a horizontal conveying device, interruption of conveyance, overlapping of substrates in basket-type treatment, and damage to the substrate during handling, are generated. Second, attributable to the substrate having low rigidity without the base plate, a finished substrate may easily warp, thus making it impossible to fulfill the demands of consumers.